This invention relates to sensing devices which utilize the gyroscopic principle, i.e., measuring the Coriolis force created by the conservation of momentum of a moving body. Specifically, the invention concerns devices called micro-gyros, which are small and inexpensive. They rely on conservation of momentum of a structure having limited oscillatory motion. They are able to withstand rough environments for long periods of time.
In this field, the terms used to describe the directions of motions and of forces can be confusing. Applicant in describing and claiming the present invention will refer to the three separate directions (Which are orthogonally related to one another) as follows: (a) the driven element, which is caused to oscillate (vibrate) at a predetermined, arbitrary rate inside the gyro moves in a linear drive direction; (b) the rotational velocity of the gyro environment in terms of angular rate, which is to be determined by the gyro, is around the rate axis; and (c) the Coriolis force, which is a function of the rotational velocity of the gyro environment, is measured by motion of a sensing element in an output direction.
Common assignee application Ser. No. 08/870,812 relates to a micro-gyro that xe2x80x9cseparates the mass (momentum of inertia) of the constant motion element driven to oscillate around the drive axis from the mass (momentum of inertia) of the variable motion sensing element which creates the measured forcexe2x80x9d. It accomplishes that result by xe2x80x9cusing: (a) an outer ring-shaped element which oscillates around the drive axis, and (b) an inner disk-shaped element which oscillates, or rocks, around the output axis as a result of the Coriolis effect.xe2x80x9d Its dual-element structure xe2x80x9cpermits the ring and the disk to be excited independently, so that each can be dynamically compensated for manufacturing tolerances by counterbalancing.xe2x80x9d
Lutz Patent No. 5,604,312 shows a rate-of-rotation sensor that uses xe2x80x9can oscillatory massxe2x80x9d moving in a linear vibrating direction, and xe2x80x9ca deflectable massxe2x80x9d caused by Coriolis force to move in a linear vibrating direction perpendicular to the motion of the oscillatory mass. Measurement of the Coriolis effect is used to determine angular velocity of the entire sensor around a rate axis, which is perpendicular to the linear vibrating directions of both masses.
The micro-gyro of the common assignee application is able to determine the external rate of rotation around either of the two (X and Y) axes which lie in the plane of the micro-gyro, but not around the third (Z) axis, which is perpendicular to the plane of the micro-gyro. The micro-gyro of the present application, like the sensor of the Lutz patent, is able to determine rate of rotation around the Z-axis, which is perpendicular to the plane of the micro-gyro.
The present invention, like Application S/N 08/870,912, separates the mass of the constant motion elementxe2x80x9d from the mass of the xe2x80x9cvariable motion sensing elementxe2x80x9d. Like Lutz Pat-5,604,312, it has an essentially rectangular arrangement, and uses perpendicular linear forces of an xe2x80x9coscillatory massxe2x80x9d, which creates the driving vibrations, and a xe2x80x9cdeflectable massxe2x80x9d, whose vibrations are measured to quantify the angular velocity of the gyro around the rate. or Z. axis.
Differences of major significance between the micro-gyro of this invention and the sensor disclosed in the Lutz patent are that in the present invention the two masses lie in the same plane, and that these movements are independent of one another. In the Lutz patent, on the other hand, the deflectable mass is mounted on top of the oscillatory mass. The Lutz structure, because of its two-tier design, is significantly more difficult and costly to manufacture, and inherently less precise in its structure. Also, its piggy-back arrangement prevents independent movement of the two masses, because the deflectable mass is constrained to move with the deflectable mass on which it is mounted.
The present invention may have its first moving element formed with an open center, i.e., formed as a rectangular xe2x80x9cringxe2x80x9d while the second moving element, formed as a rectangular xe2x80x9cplatexe2x80x9d, may be located within the open center area of the first element. The outer element, having greater mass, is the oscillatory mass, and the inner clement is the deflectable mass, which is moved by the Coriolis force.
An important practical advantage of the present invention is its manufacturing process, in which the two masses may be simultaneously formed by deposition of material on the substrate, followed by photolithography steps to define the separate elements.
In the present invention, the two masses are connected to, and supported by, anchors formed on the substrate. The connecting members are flexures (or links) which are compliant, i.e., permit relatively free motion, in the desired direction, and which are very stiff, i.e., permit substantially zero motion, in other directions. The purpose is to have a maximum transmission of vibration (oscillation) energy solely in the appropriate direction.
A preferred arrangement has one or more anchors supporting both the inner sensing element and the outer driving element. Each anchor is connected by a flexure to the inner element to support the inner element, while permitting it to oscillate in a linear direction. Each anchor-connected flexure is connected by a flexure to the driving element, in order to support the outer element, and also to transmit Coriolis force to the inner element. The outer element is driven to oscillate in a direction which is co-planar with, but perpendicular to, the force on the inner element.
In a first aspect, the invention may be regarded as a unitary three-axis micro-gyro structure that comprises: a monolithic substrate, and three micro-gyro devices formed simultaneously as a layer on the substrate by successive steps of depositing material, delineating desired material shapes by lithography, and etching to remove unwanted material, the first micro-gyro device being so constructed as to measure angular velocity of the micro-gyro structure around a first rate axis extending in the plane of the micro-gyro, the second micro-gyro device being so constructed as to measure angular velocity of the micro gyro structure around a second rate axis extending in the plane of the micro-gyro and perpendicular to the first rate axis; and the third micro-gyro device being so constructed as to measure angular velocity of the micro-gyro structure around a third rate axis perpendicular to the plane of the micro-gyro.
In a second aspect, the invention may be regarded as a three-axis micro-gyro structure comprising: first and second micro-gyro devices that measure angular velocity around first and second rate axes extending in a plane of the micro-gyro structure; and a third micro-gyro device that measures angular velocity around a third rate axis perpendicular to the plane of the micro-gyro structure.
In a third aspect, the invention may be regarded as a three-axis micro-gyro structure comprising: first and second micro-gyro devices that are substantially identical in construction, the first and second micro-gyro devices being constructed as to measure angular velocity of the micro-gyro structure around first and second rate axes extending in a plane of the micro-gyro structure, the first and second micro-gyro devices being oriented relative to one another in a plane of the micro-gyro structure to position the second rate axis perpendicular to the first rate axis; and a third micro-gyro device being constructed as to measure angular velocity of the micro-gyro structure around a third rate axis perpendicular to the plane of the micro-gyro structure.
In a fourth aspect, the invention may be regarded as a three-axis micro-gyro structure comprising: a planar substrate; a first micro-gyro device supported by the planar substrate and constructed as to measure angular velocity around a first rate axis extending in the plane of the substrate, a second micro-gyro device supported by the planar substrate and constructed as to measure angular velocity around a second rate axis extending in the plane of the substrate and perpendicular to the first rate axis; and a third micro-gyro device supported by the planar substrate and constructed as to measure angular velocity of the micro-gyro structure around a third rate axis perpendicular to the plane of the substrate.
In a fifth aspect, the invention may be regarded as a method of measuring angular velocity about three orthogonal axes comprising the steps of: providing first, second and third micro-gyros on a planar substrate; orienting the first micro-gyro to measure angular velocity about a first axis parallel to the substrate; orienting the second micro-gyro to measure angular velocity about a second axis perpendicular to the first axis and parallel to the substrate; and orienting the third micro-gyro to measure angular velocity about a third axis perpendicular to the substrate.